Drummondville had the second overall pick in the 2008 QMJHL Entry Draft, and picked Couturier after defenseman Brandon Gormley was selected by the Moncton Wildcats. Couturier joined Drummondville for the 2008–09 season and helped the team win their first President's Cup as QMJHL champions. He was tenth on the team in points during the regular season.[4]

In 2009–10, Couturier stepped forward to lead the QMJHL in points; he had the lowest point totals required to win the Jean Béliveau Trophy as leading scorer in QMJHL history. Nicolas Deschamps had the same number of points but had scored fewer goals. Teammate Gabriel Dumont was the leading QMJHL goalscorer while Couturier was fourth in the goalscoring race (also trailing Luke Adam of the Montreal Junior Hockey Club and Drummondville teammate Mike Hoffman). In the 2010 playoffs, Drummondville advanced to the semi-finals before being eliminated by the eventual champions, the Moncton Wildcats. Couturier was third on his team in points for the playoffs, behind Dumont and Chris DiDomenico.

In 2010–11, Couturier had a bout with mononucleosis over the off-season, a condition that usually takes a year to fully recover from.[5] Despite this setback, Couturier once again had an impressive year. Couturier matched the 96 points he scored the year before in 10 fewer games, leaving him fourth overall in QMJHL scoring, while having the highest points per game of any draft eligible CHL player. In the playoffs, Drummondville advanced to the second round, before being eliminated in seven games by the Gatineau Olympiques, who would continue on to the President's Cup final. Couturier finished the playoffs with 11 points in 10 games.

Couturier made an impression in training camp and started the 2011–12 season with the Flyers, also receiving ice time on the penalty kill. He earned his first point in the NHL in his third game on October 12 against the Vancouver Canucks with a primary assist on a goal by Jakub Voráček. Couturier scored his first NHL goal in his fifth game on October 18, 2011, against Craig Anderson of the Ottawa Senators in a 7–2 win.[8] He was one of the youngest players to participate in the NHL All-Star Game festivities, named on the rookie team and participating in the skills competition.[9]

During the Flyers' opening-round playoff series against the Pittsburgh Penguins, Couturier was tasked with shutting down Art Ross Trophy winner Evgeni Malkin. Couturier earned much praise for his play, holding Malkin to one even strength point while Couturier was on the ice during the series,[10] and also scoring his first career hat-trick, becoming the second-youngest player to score a hat-trick in a playoff game,[11] and adding an assist in a four-point performance during game two of the series. Teammate Jaromír Jágr compared Couturier to Hockey Hall of FamerRon Francis.[12]

To start the 2017–18 season, head coach Dave Hakstol placed Couturier on the top line with Claude Giroux and Jakub Voráček.[13][14] This move helped Couturier gain confidence and as the season progressed, he improved his offensive play.[15] On March 20, 2018, Couturier recorded his 100th career NHL goal, becoming the seventh player from his draft class to reach that milestone.[16] Couturier was awarded the Pelle Lindbergh Memorial Trophy for most improved player at the end of the regular season after he recorded a career-high 76 points.[17] He was also awarded the Yanick Dupre Class Guy Memorial Award as most sportsmanlike player and the Gene Hart Memorial Award.[17] His offensive and defensive success helped the Flyers to the 2018 Stanley Cup playoffs and earned him a nomination for the Frank J. Selke Trophy for the first time in his career.[18] He finished second in the voting to the eventual winner, Anže Kopitar.[19] In practice before Game 4 of the 2018 Stanley Cup playoffs, Couturier collided with teammate Radko Gudas, forcing him to miss Game 4.[20] Upon his return, after missing just one game, Couturier scored the game-winning goal with just over a minute to play and added an assist in Game 5. In Game 6, he tallied three goals and two assists, totalling seven points in the two games following his return. His hat-trick in Game 6 was the second of his career in the playoffs, as his first was in the 2012 Eastern Conference Quarterfinals against Pittsburgh.[21] After a series-ending 8–5 defeat in Game 6, it was announced Couturier tore his MCL in practice in his collision with Gudas, yet still continued to play in the playoffs.[22][23]

On August 22, 2018, during the off-season, Couturier suffered a knee injury unrelated to the injury in the playoffs of the previous season, keeping him out four weeks.[24] On October 9, Couturier was named an alternate captain for the Flyers on home ice, replacing Valtteri Filppula, who signed with the New York Islanders during the off-season.[25] Couturier scored his first career regular season hat trick on January 16, 2019, against the Boston Bruins.[26]

On April 29, 2019, Couturier was named to the Team Canada roster for the 2019 IIHF World Championship held in Slovakia.[31] On May 10, 2019 he was designated an alternate captain, along with Mark Stone.[32] Couturier helped Canada progress through to the playoff rounds, reaching his third consecutive final before losing to Finland to finish with the Silver Medal on May 26, 2019.[33] He finished the tournament posting 1 goal and 4 points in 10 games.